xbt::signal<void(Actor const&, Host const& previous_location)> s4u::Actor::on_host_change;
xbt::signal<void(Actor const&)> s4u::Actor::on_termination;
xbt::signal<void(Actor const&)> s4u::Actor::on_destruction;
xbt::signal<void(Actor const&, Host const& previous_location)> s4u::Actor::on_host_change;
xbt::signal<void(Actor const&)> s4u::Actor::on_termination;
xbt::signal<void(Actor const&)> s4u::Actor::on_destruction;